Internal combustion engines, for example, diesel engines, gasoline engines, or natural gas engines employ turbochargers to deliver compressed air for combustion in the engine. A turbocharger compresses air flowing into the engine, helping to force more air into the combustion chambers of the engine. The increased supply of air allows increased fuel combustion in the combustion chambers of the engine, resulting in increased power output from the engine.
A typical turbocharger includes a shaft, a turbine wheel attached to one end of the shaft, a compressor impeller connected to the other end of the shaft, and bearings to support the shaft. Often a turbine housing surrounds the turbine wheel and a separate compressor housing surrounds the compressor impeller. In addition, the turbocharger may include a bearing housing that surrounds the bearings and includes features that help prevent leakage of bearing lubrication oil into the turbine housing or the compressor housing. The turbine housing, the compressor housing, and the bearing housing are attached to each other via fasteners or other clamping mechanisms.
Hot exhaust from the engine flows through the turbine housing and expands over the turbine wheel, rotating the turbine wheel and the shaft connected to the turbine wheel. The shaft in turn rotates the compressor impeller. Relatively cool air from the ambient flows through the compressor housing where the compressor impeller compresses the air and drives the compressed air into the combustion chambers of the engine.
Because the exhaust from the engine is significantly hotter than the ambient air, the turbine wheel and the turbine housing can experience temperatures significantly higher than the other components of the turbocharger, such as the bearing housing and the compressor housing. Also, the turbine wheel may have a relatively smaller mass and may be symmetric, whereas the turbine housing may have a relatively larger mass and may be asymmetric. As a result, the turbine housing may increase in temperature more slowly than the turbine wheel, thereby resulting in thermal lag compared to the turbine wheel. Also, both the turbine housing and the turbine wheel may experience thermal expansion, but, because the turbine housing may be asymmetric, the turbine housing may expand asymmetrically. Asymmetric expansion may cause a tip clearance between the turbine wheel and the turbine housing to vary around the turbine wheel so that there may be relatively larger tip clearances in some locations around the turbine wheel, which may reduce the efficiency of the turbocharger.
One attempt to address some of the problems described above is disclosed in U.S. Pat. No. 8,322,978 issued to Dilovski et al. on Dec. 4, 2012 (“the '978 patent”). In particular, the '978 patent discloses a turbocharger including a guide vane cage clamped between a turbine housing and a bearing housing of the turbocharger without fixedly connecting the guide vane cage to either one of the two housings. The guide vane cage may be directly exposed to hot exhaust gases and may be subject to thermal expansion. An axial gap may be formed between the guide vane cage and the turbine housing so that the hot exhaust gas may flow around the guide vane cage, which may allow the guide vane cage to be heated generally uniformly, which may reduce the temperature gradient in the guide vane cage.
Although the turbocharger disclosed in the '978 patent attempts to reduce the temperature gradient in the guide vane cage surrounding the turbine wheel, the disclosed turbocharger may still be less than optimal. For example, the geometry of the turbine wheel and the guide vane cage may not provide tip clearances that are sufficiently small enough to achieve efficient turbocharger performance. Also, the clamping of the guide vane cage between the turbine housing and the bearing housing may not sufficiently isolate the guide vane cage from the turbine housing and may not allow the guide vane cage to respond fast enough to temperature changes, which may cause the blades of the turbine wheel to expand and rub against the guide vane cage.
The turbocharger of the present disclosure solves one or more of the problems set forth above and/or other problems of the prior art.